Hidrobiológica 2008, 18 (2): 155-165 Geochemical composition of surface sediments near Isla de Sacrificios coral reef ecosystem, Veracruz, Mexico Composición geoquímica de sedimentos superficiales alrededor del ecosistema arrecifal de Isla de Sacrificios, Veracruz, Mexico Leticia Rosales-Hoz, Juan Jose Kasper-Zubillaga, Arturo Carranza- Edwards, Omar Celis Hernández Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México. Apdo. Postal 70305 México 04510, DF. México. Dr. Arturo Carranza Edwards [email protected] Tel. : 56225692 Rosales-Hoz L., J. J. Kasper-Zubillaga, A. Carranza- Edwards and O. Celis Hernández. 2008. Geochemical composition of surface sediments near Isla de Sacrificios coral reef ecosystem, Veracruz, Mexico. Hidrobiológica 18 (2): 155-165. ABSTRACT Twenty three surface sediment samples were collected in the area surrounding the Isla de Sacrificios located in the southwestern Gulf of Mexico. The temporal impact of natural discharges in the area was evaluated through the study of the textural and chemical characteristics of the sediments that surround the Veracruz Reef System. The particle size during the three sampled seasons was associated with the prevailing energy conditions. The degree of influence of terrigenous sediments was evaluated through the content of Al2O3, SiO2, Na2O and K2O, which is higher in October (2004) compared to June (2004) and/or February (2005) due to the rainy season. It was observed that gravel, CaO and CO3 were significant variables grouped in Factor 1 that suggested that gravel-sized fractions are produced by the abrasion of the reef in February (2005) and being correlated with other variables in June (2004). Another groupings were among SiO2, CaO, K2O, CO3, for October (2004) which suggested dilution of carbonates due to the terrigenous input. In addition, the factor analysis showed that grain size and heavy minerals represented by TiO2, MnO, MgO and Fe2O3 have a major importance in February (2005) associated with fluvial discharges. The factor analysis showed that the sedimentological and geochemical characteristics of the sediments varied throughout the different seasons. A correlation among Al2O3 and Na2O, P2O5, y Fe2O3 and organic carbon in the three sampling seasons suggested that these chemical components have a terrigenous source. Keywords: Reef, terrigenous, sediments, Gulf of Mexico RESUMEN Se estudiaron veintitrés muestras de sedimento superficial, colectadas en los alrededores de la Isla de Sacrificios, ubicada al suroeste del Golfo de México. El impacto temporal de las descargas naturales fue evaluado a través de las características texturales y químicas de los sedimentos que rodean al SAV. El tamaño de partículas de los sedimentos en las tres estaciones del año estuvo en función con las condiciones de energía prevalecientes en la zona. El grado de influencia de los sedimentos terrígenos se determinó por el contenido de Al2O3, SiO2, Na2O y K2O, siendo mayor en octubre (2004) que en febrero (2005) o junio (2004) y estuvo asociado con la temporada de lluvias. Se observó que la grava, CaO y CO3 fueron variables significativas agrupadas en el Factor 1 en octubre (2004) lo cual sugirió que las 156 Rosales-Hoz., et al. fracciones tamaño grava fueron posiblemente originadas por la abrasión del arrecife en febrero (2005) reflejando su relación con otras variables para Junio (2004). Otras agrupaciones fueron observadas entre las variables SiO2, CaO, K2O, CO3 lo cual indicó que la dilución de carbonatos es por influencia de terrígenos. El análisis factorial mostró que el tamaño de grano y minerales pesados representados por TiO2, MnO, MgO y Fe2O3 tuvieron una mayor importancia en febrero (2005) asociados con descargas fluviales. Al análisis factorial reflejó que las características sedimentológicas y geoquímicas de los sedimentos varían estacionalmente. La correlación entre Al2O3 y Na2O, P2O5, y Fe2O3 y carbón orgánico sugiere que estos compuestos químicos tienen una fuente terrígena. Palabras clave: Arrecife, terrígeno, sedimentos, Golfo de México. INTRODUCTION perimeter of 53,770 m2 and 917.3 m, respectively and 1.56 km away from the coast. On the other hand, the Isla de Sacrificios Reef has Coral Reefs in the southwestern Gulf of Mexico at Veracruz an area and perimeter of 397,630 m2 and 2,745 m respectively. are well-developed environments of reef islands or barriers close to the coastline. Coral reefs are sensitivities to sediment dischar- Depths near the Isla de Sacrificios range from 8 m to 15 m ges, sea-water temperature and salinities changes, and global (Fig. 1). Coastal currents surrounding the study area are in avera- warming effect (Shen & Boyle, 1988; Linn et al., 1990; Allison, 1996; ge 3 cm s-1 with northwesterly and easterly components in winter Ramos et al., 2004). The Veracruz coastal area is characterized by and summer respectively (Fernández-Eguiarte et al., 1992 a, 1992 the presence of the Veracruz Reef System (VRS) that apparently b). Dominant winds come from the north and northwestern part of has been subjected to an environmental impact due to natural river the Gulf of Mexico with average velocities ranging from 6 m s-1 to discharges of terrigeneous sediments and industrial activities. 8 m s-1 in February, June and October. Northerly winds dominate more than 60 % of the time in February. The rainy and dry seasons Additionally, untreated sewage coming from domestic and correspond to a period from July to October and from April to industrial sources which carry organic carbon, nutrients, and May respectively. heavy metals is affecting the preservation and life of the VRS (Ramos et al., 2004). MATERIAL AND METHODS The aim of the present work is to analyze the degree of influence of terrigenous discharges in the area in superficial Surface sediments were collected at 23 different sites near bottom sediments surrounding the VRS based upon the texture the Isla de Sacrificios area. In addition, sediment samples from and chemistry of the sediments. The importance of this paper is the Jamapa River mouth were taken in order to have a chemical to highlight the effect that the presence of terrigenous input may control over the adjacent land. Three sampling trips were carried have in the VRS. out on June (2004), October (2004) and February (2005). Samples were taken with a van veen dredge and sediment samples were removed from the superficial middle part of each sample to STUDY AREA avoid the contact of the sediments with the metallic walls of the dredge. Sediments were transferred to plastic bags and kept at The VRS is located along the coast of Veracruz, southwes- 4°C until analysis. tern Gulf of Mexico, Mexico. The northern region of the VRS com- prises 10 reefs located in front and south of the Port of Veracruz The grain size distribution of the sediment samples was respectively. In present time, the VRS has unfavorable conditions determined by means of Coulter LS230 laser equipment. Four for reef development due to its closeness to the Port of Veracruz granulometric groups were identified: gravel, sand, clay and silt. and to river discharges that carry important amounts of water. Mean graphic size (Mz') and sorting (T') were obtained follo- For instance, La Antigua River is located on a basin of 2 880 km2 wing the formulas and limits proposed by Folk (1974). with an annual average volume of 2,817,000 m3. Another fluvial Sediment samples for chemical analysis were dried at systems like the Jamapa River, located on a basin of 3350 km2 55°C for 48 hours, and homogenized in a SPEX 8000 mixer/mill has an average annual drain of 1,895,000 m3 and the Papaloapan using tungsten-carbide vials. Organic carbon was measured by River on a basin of 39,189 km2 has an average annual volume of oxidation with potassium dichromate according to the method 39,175,000 m3 (Tamayo, 1991). It seems that these fluvial systems described by Gaudette et al. (1974). The coefficient of variation have an impact in the development and preservation of the VRS of the organic carbon determination was 2.64%. Carbonate was (Rivera-Ramirez, 2007). measured by back titration of an excess of hydrochloric acid At the Northern portion of the VRS is located the Isla de with sodium hydroxide based on the method by Hesse (1971). The Sacrificios (19°10’ 27” N; 96° 05’ 31 W) (Fig. 1) covering an area and coefficient of variation of carbonate determination was 1.86 %. Hidrobiológica Sediments in Sacrificios Island 157 Figure 1. Study area. Location of the sampling sites and bathymetry. Analyses of major elements were made by using an X Ray Sacrificios reef suggests low energy conditions in this area allo- Fluorescence sequential system, model Siemens SRS 3000. wing the deposition of fine sediments. The area between the Isla Accuracy of the analyses was measured by the use of reference de Sacrificio and Pajaros reef is a potential non-exposed region material the coefficient of variation obtained were: SiO2: 1.18 %. from the northerly winds and high energy of the waves. Al2O3: 9.66 %, Fe2O3: 1.88 %, MnO:1.82 %, MgO: 2.0 %, CaO: 3.75 %, The samples collected at Jamapa River Estuary showed an Na O: 1.98 %, K O: 1.34 %, TiO : 2.6 % and P O : 5.5 %. Correlations 2 2 2 2 5 average Mz' value of 1.29 ' in June (2004). However, a differen- between organic carbon, SiO , Al O and depth were carried out 2 2 3 ce in Mz' values was observed at sampling points J4 and J5 (Mz (Fig. 2) as well as parameters distributions (Fig. 3). = 1.183' and 5.236', respectively) in October (2004). Low Mz' values correspond to coarser grains that were located further to the fluvial mouth, whilst fine-sized samples are imparted by the RESULTS AND DISCUSSION turbulence of high wave energy as well as by an excess of sus- Table 1 shows the textural parameters of the sediments pended fine sediments related to the rainy season.